1. Technical Field
This application relates to computer storage, and more particularly to the field of partitioning computer storage.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek, all of which are incorporated by reference herein. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels to the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical devices (also referred to as “logical volumes”). The logical devices or may not correspond to the actual disk drives. Allowing multiple host systems to access the single storage device allows the host systems to share data stored therein.
FIG. 1 is a diagram 20 that shows a host 22, a conventional local storage device 24 and a conventional remote storage device 26. The host 22 reads and writes data from and to the local storage device 24 via a host adapter (HA) 28, which facilitates the interface between the host 22 and the local storage device 24. Although the diagram 20 only shows one host 22 and one HA 28, it is also possible to use multiple HA's and it is also possible that one or more HA's may have one or more hosts coupled thereto.
Data from the local storage device 24 is copied to the remote storage device 26 via an RDF link 29 to cause the data on the remote storage device 26 to be identical to the data on the local storage device 24. Although only the one link 29 is shown, it is possible to have additional links between the storage devices 24, 26 and to have links between one or both of the storage devices 24, 26 and other storage devices (not shown). Note that there may be a time delay between the transfer of data from the local storage device 24 to the remote storage device 26, so that the remote storage device 26 may, at certain points in time, contain data that is not identical to the data on the local storage device 24. Communication using RDF is described, for example, in U.S. Pat. No. 5,742,792, which is incorporated by reference herein.
The local storage device 24 includes a first plurality of RDF adapter units (RA's) 30a, 30b, 30c and the remote storage device 26 includes a second plurality of RA's 32a-32c. The RA's 30a-30c, 32a-32c are coupled to the RDF link 29 and are similar to the host adapter 28, but are used to transfer data between the storage devices 24, 26.
The storage devices 24, 26 may include one or more disks, each containing a different portion of data stored on each of the storage devices 24, 26. FIG. 1 shows the storage device 24 including a plurality of disks 33a, 33b, 33c and the storage device 26 including a plurality of disks 34a, 34b, 34c. The RDF functionality described herein may be applied so that the data for at least a portion of the disks 33a-33c of the local storage device 24 is copied, using RDF, to at least a portion of the disks 34a-34c of the remote storage device 26. It is possible that other data of the storage devices 24, 26 is not copied between the storage devices 24, 26, and thus is not identical.
Each of the disks 33a-33c is coupled to a corresponding disk adapter unit (DA) 35a, 35b, 35c that provides data to a corresponding one of the disks 33a-33c and receives data from a corresponding one of the disks 33a-33c. Similarly, a plurality of DA's 36a, 36b, 36c of the remote storage device 26 are used to provide data to corresponding ones of the disks 34a-34c and receive data from corresponding ones of the disks 34a-34c. An internal data path exists between the DA's 35a-35c, the HA 28 and the RA's 30a-30c of the local storage device 24. Similarly, an internal data path exists between the DA's 36a-36c and the RA's 32a-32c of the remote storage device 26. Note that, in other embodiments, it is possible for more than one disk to be serviced by a DA and that it is possible for more than one DA to service a disk.
The local storage device 24 also includes a global memory 37 that may be used to facilitate data transferred between the DA's 35a-35c, the HA 28 and the RA's 30a-30c. The memory 37 may contain tasks that are to be performed by one or more of the DA's 35a-35c, the HA 28 and the RA's 30a-30c, and a cache for data fetched from one or more of the disks 33a-33c. Similarly, the remote storage device 26 includes a global memory 38 that may contain tasks that are to be performed by one or more of the DA's 36a-36c and the RA's 32a-32c, and a cache for data fetched from one or more of the disks 34a-34c. 
The storage space in the local storage device 24 that corresponds to the disks 33a-33c may be subdivided into a plurality of logical devices (also referred to as “logical volumes”). The logical devices may or may not correspond to the physical storage space of the disks 33a-33c. Thus, for example, the disk 33a may contain a plurality of logical devices or, alternatively, a single logical device could span both of the disks 33a, 33b. Similarly, the storage space for the remote storage device 26 that comprises the disks 34a-34c may be subdivided into a plurality of logical volumes or logical devices, where each of the logical devices may or may not correspond to one or more of the disks 34a-34c. 
FIG. 2 is a diagram 40 that illustrates an embodiment of the storage device 24 where each of a plurality of directors 42a-42c are coupled to the memory 37. Each of the directors 42a-42c represents one of the RA's 32a-32c, the HA 28, and/or the DA's 38a-38c. In some cases, there may be up to sixtyfour directors coupled to the memory 37, but in other instances there may be a higher or lower maximum number of directors that may be used.
The diagram 40 also shows an optional communication module (CM) 44 that provides an alternative communication path between the directors 42a-42c. Each of the directors 42a-42c may be coupled to the CM 44 so that any one of the directors 42a-42c may send a message and/or data to any other one of the directors 42a-42c without needing to go through the memory 37. The CM 44 may be implemented using conventional MUX/router technology where a sending one of the directors 42a-42c provides an appropriate address to cause a message and/or data to be received by an intended receiving one of the directors 42a-42c. Some or all of the functionality of the CM 44 may be implemented using one or more of the directors 42a-42c so that, for example, the directors 42a-42c may be interconnected directly with the interconnection functionality being provided on each of the directors 42a-42c. In addition, a sending one of the directors 42a-42c may be able to broadcast a message to all of the other directors 42a-42c at the same time.
In the conventional design illustrated by FIG. 1 and FIG. 2, all of the directors share common resources, such as the memory 37, even though the storage device 24 may be used in environments where different unrelated hosts and/or different groups of hosts are performing unrelated activities and thus, do not share any logical storage devices. Such an arrangement may be inefficient in some cases and may even require active allocation of resources, which adds to overhead. Furthermore, since the conventional system illustrated by FIG. 1 and FIG. 2 uses a single operation system to manage the various components of each of the storage devices, then any change to the operating system (e.g., upgrade) would affect the entire storage device 24 and all of the hosts coupled to the storage device 24.
Thus, it is desirable to be able to partition a storage device in a way that eliminates the need for unrelated hosts or groups of hosts to compete for resources and allows for separately modifying the system of each partition in a way that minimizes the effect on other partitions.